In the biophysics of membrane processes, there is a wide current interest in the possibility that membrane constituents undergo molecular orientation and conformational changes during membrane function, and that many membranes consist of mosaics, some parts of which are fluid. Among the forces which relate to orientation and conformation changes, the transmembrane electric field acting on dipolar membrane constituents, is of particular interest. However, there appears to be no data on polarization effects in appropriate two-dimensional analogous structures, on which to base quantitative arguments as to the relevance and magnitude of such effects in biomembranes. Following a recent thermodynamic analysis of the effects of electric fields at liquid surfaces containing monolayers, calculations of surface polarisabilities are available in principle via new Maxwell relations. Furthermore, the analysis has predicted certain phenomena not yet observed experimentally, in which applied electric fields are predicted to alter phase behavior in films, and to cause pressure and composition variations. It is proposed to demonstrate these new phenomena, to extend the thermodynamics to multicomponent two-dimensional systems and model membranes, and to use the effect of fields on monolayers to give much deeper insight into the behavior of two-dimensional micelles, or aggregates such as are found in higher-order phase transitions analogous to those found in some membranes exhibiting fluidity. The proposal is therefore twofold in its objective - to demonstrate some new phenomena and to develop basic concepts in the surface chemistry of monolayers; and to provide a phenomenological basis for the description of field-dependent processes in biomembranes. The methods to be used will be extensions of current techniques for measuring surface variables for monolayer films.